Flow meters, provers, and flow proving components utilize a known traceable volume to simulate actual operating conditions and to test and verify their performance. A SVP (Small Volume Prover), or piston prover, can be employed to accurately measure flow in a fluid flow process and to calibrate, for example, a flow measurement device employed in custody transfers, pipe lines, etc. Small volume provers generally include a precision bore cylinder with sensors that detect the initiation and termination of the stroke of a piston. The piston is driven upstream against the fluid flow and then released to travel with the fluid flow to measure the flow rate of the fluid.
Small volume provers typically include a piston rod connected to the piston that protrudes outside the prover in order to pull the piston to an upstream position by an external motor. FIG. 1 illustrates a perspective view of a prior art small volume prover 100 having a piston rod 135 that exits the prover 100. The small volume prover 100 includes a cylinder 120 having a flow inlet 110 and a flow outlet 190. A piston 130 configured with a poppet valve arrangement 140 is located within the bore cylinder 120. The piston 130 can be driven upstream via the external motor connected to the piston rod 135 that exits a prover housing 195. The external rod 135 can be sealed to the prover housing 195.
One of the problems associated with such prover designs is that the piston rod seal can leak temporarily from contaminant interference contained within the fluid, contaminants outside the prover volume, or forces of the rod 135 on the prover seals; and as a result, seal wear and/or damage can occur during operation of the prover 100. Additionally, such a rod seal can leak as the rod 135 moves in and out of the cylinder 120, particularly if the fluid has a low viscosity, lubricity, and temperature. For example, in the case of LNG (Liquefied Natural Gas), the leaking fluid is flammable and can cause a potential environmental hazard. Furthermore, seal leakage results in inaccurate flow measurement.
Based on the foregoing, it is believed that a need exists for an improved piston prover apparatus and method for providing accurate position measurement, as will be described in greater detail herein.